This invention relates to a printer and a facsimile apparatus using the printer and, more particularly to a printer which prints an image on a print medium in accordance with and ink-jet printing method and a facsimile apparatus using the printer.
An ink-jet printer which performs printing by discharging ink droplets from a printhead, comprising a plurality of nozzles, on a print medium such as a print sheet or an OHP sheet, in accordance with an ink-jet printing method, has advantages such as low running cost, suitability for color printing, and quiet print operation. Therefore, the ink-jet printer is widely used as a printing unit of facsimile apparatuses, copying machines and the like, as well as an output device of computers.
Further, as a printhead of this printer, a monochrome printhead which performs monochrome printing by using only one color ink, e.g., black ink, and a color printhead which supplies yellow, magenta, cyan and black color ink and performs color printing by discharging ink from nozzles assigned to the respective colors have been provided.
Upon applying the printer to a facsimile apparatus, for printing based on received facsimile image information, a mechanism to detect print-disable status such as ink exhaustion and ink-discharge failure is provided. That is, in the conventional technique, to avoid omission of image printing due to ink exhaustion during image printing using received facsimile image data, existence/absence of ink is judged after printing of one page. If it is judged that ink remains, data corresponding to printed image is deleted from an image memory. For this judgment, the printer has a photosensor (photo-interrupter) including a light-emission device comprising an LED or the like and a photoreception device comprising a photo-transistor or the like. As ink-discharge status detection, ink-discharge failure status due to ink exhaustion or status where nozzles are clogged with some foreign materials due to some reasons and printing is not normally performed, is detected by discharging ink so as to interrupt light from the light-emission device, and monitoring change of the light received by the photoreception device.
FIG. 15 is a cross-sectional view showing the structure of a printer included in a facsimile apparatus.
As shown in FIG. 15, a plurality of print sheets P are piled on a cassette 151, and taken out by a paper-feed roller 152, one by one, to a conveyance roller 153, and further, to a printer B. The printer B has a printhead 160 which performs printing in accordance with an ink-jet printing method and which is scanned in a direction (main-scanning direction) orthogonal to a print-sheet conveyance direction. The printhead 160 comprises a large number of nozzles (e.g. 128) in a direction orthogonal to the main-scanning direction (X direction in FIG. 15 is the subscanning direction). Image printing is made by discharging ink from the printhead 160 on the surface of the print sheet P while scanning the printhead 160 in the main-scanning direction. After the completion of image printing, the print sheet P is conveyed by a pair of discharge rollers 154 along a guide 155 in the X direction, and discharged by a discharge roller 156, a discharge rod 157, onto a discharge stacker 158, and stacked there.
The printhead 160 mounted to this apparatus is a cartridge type printhead which includes an ink tank. When ink is exhausted, the printhead can be exchanged for a new printhead with an ink tank. To attain color printing with downsizing of the apparatus main body, the printhead 160 has 64 nozzles to discharge black ink, and respectively 24 nozzles to discharge ink of primary three colors, yellow, cyan and magenta. The respective color ink can be replenished by independently changing small separate ink tanks of respective colors.
Upon applying the printer having this construction to a facsimile apparatus, to ensure print-output of received image information, it is necessary to detect print-disable status such as ink exhaustion and ink-discharge failure. As a method for detection, a technique to directly discharge ink between a light-emission device and a photoreception device constituting a photo-interruptive type photosensor has been proposed. The change of output from the photosensor caused by interruption of light from the light-emission device by the discharged ink is detected and ink-discharge abnormality can be judged based on the result of detection.
In the photo-interruptive type photosensor, a lens is integrally molded on a light-emitting surface, so that the light-emission device can irradiate light in approximately parallel toward a photoreception device such as a photo-transistor. On the other hand, the photoreception device has a 0.7.times.0.7 mm hole formed of a mold member, on the optical axis, on its photoreception surface. That is, a detection area is narrowed to 0.7 mm in height and 0.7 mm in width between the photoreception device and the light-emission device. The optical axis connecting the light-emission device and the photoreception device is set to parallel to the nozzle array of the printhead. The interval between the light-emission device and the photoreception device is wider than the nozzle array of the printhead. When the optical axis and the position of the nozzle array coincide, all ink droplets discharged from the nozzles of the printhead pass the detection area between the light-emission device and the photoreception device. As the ink droplets pass the detection area, the ink droplets interrupt light from the light-emission side, and decrease light intensity to the photoreception side, thus the output from the photo-transistor as the photoreception device changes. Since the number of nozzles to discharge ink is approximately proportional to the amount of change of the output from the photosensor, if the variation of the output from the photosensor is equal to a predetermined threshold value or greater, it is judged that ink remains, i.e., "print operation has been normally performed". In contrast, if the variation of the output from the photosensor is less than the threshold value, it is judged that ink-discharge is poor, i.e., "print operation has not been normally performed". In this case, further print operation is suspended until recovery operation such as ink-tank change is made, and facsimile reception is stopped or received data is stored into an image memory.
The ink-discharge status detection using the photo-interruptive type photosensor as described above is made such that after the completion of printing for one page of print sheet, ink is simultaneously discharged from all the nozzles necessary for facsimile reception printing, e.g., 64 black-ink nozzles.
Further, in case of judgment of existence/absence of ink with respect to color ink based on the amount of change of output from the photosensor, the judgment is made by using a threshold value common to the respective colors. For the judgment, to improve detection precision, the amount of ink to be discharged is changed in accordance with ink color.
However, when the color printhead is attached to a conventional facsimile apparatus for monochrome image printing, to print an image based on received image data on a print medium, black ink is discharged from only the nozzles assigned to black ink. Accordingly, in comparison with a printhead for monochrome printing (monochrome printhead), the number of black-ink nozzles is smaller. Even if all the nozzles assigned to black ink are used for discharging black ink, ink-discharge amount differs in the two type of printheads, and the degree of interruption of light from the light-emission device differs in the printheads. As a result, an output signal from a photo-transistor used for judgment of existence/absence of ink varies in accordance with the type of printhead attached to the apparatus.
Accordingly, the comparison of the output signal from the photo-transistor with one threshold value cannot attain exact judgment of existence/absence of ink.
Regarding the printer according to an ink-jet printing method, to further utilize the advantage of the printing method, it has a print mode (normal print mode) for discharging ink from all the nozzles of a printhead to form an image and another print mode (economy print mode) for discharging ink from alternate nozzles to form an image with only the half amount of ink used in normal print mode.
On the other hand, residual-ink detection and ink-discharge status detection in the conventional printer is made by discharging black ink necessary for printing based on received facsimile data from all the nozzles assigned to black ink. Even when facsimile-reception printing is performed in the economy print mode, judgment of ink-discharge status on nozzles which are not related to image formation is included in judgment of normal/abnormal printing status.
However, assuming that an average value of the amount of change of the output, obtained from the photoreception device, in case of normal ink discharge from 60% of the all nozzles, is employed as a threshold value for judgment of normal/abnormal print operation, if facsimile-reception printing is performed in the economy print mode, and 30% of all the nozzles are in poor ink-discharge status, further, if most of those poor nozzles are used in actual printing, a control circuit of the facsimile apparatus judges that printing has been normally performed and deletes image data stored in an image memory.
If print operation is performed in the normal print mode, a printed image includes faint portions at about 30%, which causes no problem for practical purpose of legibility; however, in the economy print mode, a printed image includes faint portions at about 60%, which disturbs interpretation of information provided by the printed image. In the latter case, as data is deleted from in the image memory, the information is entirely lost.
Further, in a case where the ink-jet printer is used as a terminal of a computer, if precision of ink-discharge status detection is low, there is a possibility that, in printing a document file of tens of pages in the economy print mode, a large number of images where information is not intelligible at all is outputted. In this case, print-output must be retried, which increases a user's labor, further, wastes resources such as print sheets and ink, as a result, raises the running cost.
In consideration of the tendency of development of current technologies, it is predicted that color facsimile apparatuses and color printers will greatly become popular in the future. Print control based on residual-ink detection must be directed to, as well as black ink, ink of three primary colors, yellow, cyan and magenta. However, detection precision of residual-ink detection for respective color ink differs in colors unless the following factors are fully considered: (1) a printhead may have a construction where the number of black-ink nozzles and those of nozzles assigned to other color ink are different; (2) light-transmittances of respective color ink are different; (3) variation of output from a photoreception device differs in respective color ink since diameter of nozzle and that of ink droplet-are different in respective color so as to form appropriate color image by adjusting tints of respective colors.
For example, as in the conventional printer, if existence/absence of ink is judged by using a threshold value common to the respective color ink, as respective light-transmittances of the respective color ink with respect to the photo-interruptive type photosensor are not considered, the detection result has low reliability. Further, if ink-discharge amount is changed in accordance with ink color, the amount of ink used for ink-discharge status detection differs for each ink color. This causes a problem that particular color ink is consumed in ink-discharge status detection and exhausted earlier than other ink.